This invention relates to compositions for and methods of reducing and eliminating injuries to organs subjected to ischemic episodes.
Liver transplantation has become an important therapy for patients with end-stage liver disease. Reperfusion injury, however, remains a serious problem that limits the use of this method. Reperfusion injury is the major cause for graft rejection, retransplantation and even mortality. Liver damage is the consequence of ischemica during organ transplantation and is triggered by reestablishing blood flow through the vascular system of the organ. This results in the generation of reactive oxygen species (ROS) by nonparenchymal cells, the development of oxidative stress, and cell demise, mostly by apoptosis in the liver. The oxidative stress occurs initially in the vasculature (and not inside the hepatic parenchymal cells) and is produced by the resident macrophages (Kupffer cells) in the liver. Subsequently, during the following hours, neutrophils can infiltrate into the liver, accumulate, and in turn can produce a second wave of ROS.
Because oxidative stress in the principal cause of reperfusion injury, a number of antioxidant therapies have been introduced to minimize damage. For example, addition of superoxide dismutase to the perfusate to degrade superoxide anion radicals, inclusion of monoclonal antibodies directed against neutrophils to prevent PMN-induced damage, or supplementation of the perfusate with glutathione as an extracellular radical scavenger and antioxidant, have been successfully used in counteracting oxidative stress-induced endothlial cell injury.
In particular, the addition of deferoxamine to the perfusate has yielded beneficial effects on reperfusion injury. Deferoxamine is a clinically used iron chelator that prevents the redox cycling of iron and thus precludes the iron-catalyzed formation of injurious hydroxyl radicals from hydrogen peroxide. Attenuation of reperfusion injury with deferoxamine has also corroborated the assumption that ROS, and in particular metal-catalyzed production of hydroxyl radicals, play a crucial role in reperfusion injury.
Unfortunately, the clinical relevance of antioxidant supplementation is limited by side effects or low efficacy. For example, deferoxamine can become toxic at high concentrations. Therefore, it is an object of this invention to provide better antioxidant strategies to antagonize reperfusion injury in liver transplantation.
It has now been discovered that the addition of tagatose to an organ storage and preservative solution might reduce reperfusion injury of the organ during surgery and/or following removal of the organ from a subject. Tagatose exerts a dual effect that is beneficial in preserving the organ and preventing reperfusion injury. First, it is an aqueous-phase antioxidant. The putative mechanism of this protective effect against oxidative cell injury is iron chelation, sequestering iron from partitioning into membranes and promoting membrane lipid peroxidation. Second, exposure of organ cells such as liver cells to tagatose massively decreases ATP. The ATP- depleting effect is beneficial in preventing apoptosis, as ATP is required for the apoptotic process to be initiated.
This invention permits the reduction of reperfusion injury in any organ, e.g., heart, kidney, intestines, liver, etc. The subject from which the organ is removed may be any mammalian species. The practice of this invention is especially useful in the transplantation of an organ from one human to another human.
The organ storage solution may include any commercial cold storage media such as Viaspan, also known as Belzer MPS, and UW (University of Wisconsin) solution.
Each L of Viaspan, which is a light yellow, sterile, non-pyrogenic solution for hypothermic flushing and storage of organs, contains: pentafraction (hydroxyethyl starch) 50 g, lactobionic acid 35.83 g, potassium phosphate monobasic 3.4 g, magnesium sulfate heptahydrate 1.23 g, raffinose pentahydrate 17.83 g, adenosine 1.34 g, allopurinol 0.136 g, total glutathione 0.922 g, potassium hydroxide q.s., sodium hydroxide adjusted to pH 7.4, water for injection q.s. The solution has an approximate calculated osmolarity of 320 mOsM, a sodium concentration of 29 mEq/L, a potassium concentration of 125 mEq/L, and a pH of approximately 7.4 at room temperature.
Preferably, the tagatose is D-tagatose and is added in an amount of from about 0.018 to about 0.36% by weight, based on the weight of the organ storage solution.